A polyoxy tetramethylene diol (hereinafter also referred to as “PTMG”) is a polymer of tetrahydrofuran (hereinafter referred to as “THF”). A urethane resin with this PTMG as a soft segment component is used for an elastic fiber, a synthetic leather, a flooring material, a printing ink binder, and so on because it is excellent in an elastic property, hydrolysis resistance, and so on.
However, PTMGs with a molecular weight ranging from 500 to 2,500, which are useful for the urethane resin, have a melting point in a range of from 20 to 40° C. Urethane resins using these PTMGs as a raw material have a problem that polyol-derived portions crystallize at temperatures below the ordinary temperature to enhance the elastic modulus (modulus) and degrade elastic recovery at low temperatures. This property might pose a problem in application to the elastic fiber. In a case where the elastic fiber is used for stockings or the like, for example, the high elastic modulus (modulus) will result in a too strong constriction and degradation of comfortableness in turn. Furthermore, in a case where this elastic fiber is used for sportswear, there is a problem that under low temperatures the stretchability becomes poor and wearability becomes poor. It becomes unsuitable for use, particularly in the winter season or under subzero temperatures like skiwear.
In order to improve the above drawbacks of PTMGs, it is proposed to use a copolymer of THF and 3-methyltetrahydrofuran (hereinafter referred to as “3Me-THF”) or a random copolymer of THF and ethylene oxide (hereinafter also referred to as “EO”) and/or propylene oxide (hereinafter referred to as “PO”) (cf. Patent Documents 1 to 5). However, with respect to the THF/3Me-THF copolymer, the polyol becomes expensive because the raw material 3Me-THF is expensive, and its heat resistance at high temperatures is insufficient. Furthermore, the THF/PO random copolymer or THF/EO random copolymer is not satisfactory in the tensile property, and a molecular weight distribution of the polyol is likely to be wide. In addition, the urethane resins using these materials as raw materials were insufficient in the elastic property and tensile property.
There are thus strong demands for a method for inexpensively producing a urethane resin with satisfactory properties with respect to all the properties including the heat resistance, elastic property, tensile property, and so on.
Patent Document 1: JP-A-63-235320
Patent Document 2: JP-A-2-19511
Patent Document 3: JP-A-2002-348727
Patent Document 4: JP-A-2002-348728
Patent Document 5: JP-A-8-511297